A ferroelectric capacitor was known in the past. The ferroelectric capacitor had a ferroelectric layer that was located between two opaque metal plates. The ferroelectric capacitor was placed in an unpolarized state, or in an electrically polarized state, by creating an electric field across the opaque metal plates.
The state of polarization of the ferroelectric layer of the known ferroelectric capacitor was electrically read out. Many electrical read-outs of an electrically polarized ferroelectric layer of the ferroelectric capacitor caused degradation in the amount of electrical polarization of the ferroelectric layer of the ferroelectric capacitor. This degradation would produce an ambiguous result during a subsequent readout of the state of electrical polarization of the ferroelectric capacitor.
The present invention relates to an optically readable ferroelectric memory cell. A translucent ferroelectric layer of the optically readable ferroelectric memory cell is electrically written into either an optically polarized state or into an optically unpolarized state. The state of the ferroelectric memory cell is optically readable. The optically readable ferroelectricmemory cell is nonvolatile. The optically readable ferroelectric memory cell does not easily lose a computer bit stored therein, when exposed to nuclear radition. Many optical readouts of the optically readable ferroelectric memory cell does not degrade the optically state of a translucent ferroelectric layer of the optically readable ferroelectric memory cell.
The disclosed optically readable ferroelectric memory cell has a translucent ferroelectic layer between two translucent metal layers. The translucent ferroelectric layer can be electrically written into either an optically polarized state or into an optically unpolarized state by respectively placing a first voltage or a second voltage between the two translucent metal layers. The second voltage is equal in magnitude but opposite in direction to the first voltage.
The disclosed optically readable memory cell has a wire grid polarizer between two translucent silicon dioxide layers. One of the translucent silicon dioxide layers is adjacent to one of the translucent metal layers. The other translucent silicon dioxide layer is adjacent to a sensing diode region. The sensing diode region is built into a semiconductor substrate. A translucent silicon dioxide passivation layer covers external portions of the other layers, to protect the optically readable ferroelectric memory cell.
Many optical readouts of the optically readable ferroelectric memory cell does not degrade the optically polarization state of the translucent ferroelectric layer of the optically readable ferroelectric memory cell. A value of a binary bit stored in the optically readable ferroelectric memory cell will not be ambiguous, after many optical readouts of the disclosed optically readable ferroelectric memory cell.
The disclosed optically readable ferroelectric memory cell is electricall written from an optically unpolarized state and an optically polarized state, by creating an electric field between the translucent metal layers. The translucent ferroelectric layer of the optically readable ferroelectric memory cell is thus electrically written into an optically polarized state or optically unpolarized state, by applying a voltage between the translucent metal layers. An optically polarized state of the translucent ferroelectric layer exhibits optical birefringence to polarized light. An electro-optic coefficient of the ferroelectric material of the translucent ferroelectric layer is changed by electrically writing the translucent ferroelectric layer into an optically polarized state.
The optically polarization state of the disclosed optically readable ferroelectric memory cell is determined by shining polarized light onto the ferroelectric memory cell. The plane of polarization of the polarized light is aligned with the plane of optical polarization of the planar wire grid polarizer of the ferroelectric memory cell. More polarized light passes onto a sensing diode region of a ferroelectric memory cell that is in an optically unpolarized state, than passes onto a sensing diode region of a ferroelectric memory cell that is in an optically polarized state. The amount of current is greater through a sensing diode region of a ferroelectric memory cell that is in an optically unpolarized state, than through a sensing diode region of a ferroelectric memory cell that is in an optically polarized state.
Again, the disclosed optically readable nonvolatile ferroelectric memory cell accommodates many optical readouts of a the optical state of the translucent ferroelectric layer. Optical readout of the disclosed ferroelectric memory cell does not degrade the optical state of a translucent ferroelectric layer of the disclosed optically readable ferroelectric memory cell.
The disclosed memory cell uses a wire grid polarizer and a sensing diode region, to detect the optically polarized state or optically unpolarazed state of the disclosed ferroelectric memory cell. The optical state is read out by shining an optically polarized light beam through the top translucent metal layer of the disclosed memory cell. If the translucent ferroelectric layer is in an optically polarized state, the incident polarized light beam is split into an ordinary ray and an extraordinary ray by the translucent ferroelectric layer. The ordinary ray is retarded by the optically polarized translucent ferroelectric layer, while the extraordinary ray is not retarded. The overall effect of the retardation is to rotate the plane of the incident polarized light beam. Rotation of a plane of polarization of the incident polarized light beam is detected by the wire grid polarizer.
If the translucent ferroelectric layer is not in an optically polarized state, the polarized light is not split. The sensing diode region detects the amount of polarized light that passes through the wire grid polarizer. More light passes through the wire grid polarizer, if the polarized light is not split than if the polarized light is split. In this manner the optical state of the optically readable nonvolatile ferroelectric memory cell is optically read out.
Again, to optically read out the optical state of the translucent ferroelectric layer, an optically polarized light beam is shined onto the disclosed optically readable nonvolatile ferroelectic memory cell. The plane of polarization of the incident polarized light beam is rotated, if the translucent ferroelectric layer is in an optically polarized state. If the translucent ferroelecric layer is in an optically polarized state, the translucent ferroelectric layer splits the incident optically polarized light beam into an ordinary light ray and an extraordinary light ray. If the translucent ferroelectric layer is in an optically polarized state, the ordinary light ray is slowed down, that is, retarded. The extraordinary light ray is not retarded. After the two rays have passed through the translucent ferroelectric layer, they form an optically polarized light beam whose plane of optical polarization has been rotated. The plane of polarization of the incident polarized light beam is not rotated, if the translucent ferroelectric layer is not in an optically polarized state.
The rotation or non-rotation of the optically polarized light beam is detected by means of the wire grid polarizer and the optical-beam-intensity sensing diode region. The plane of polarization of the incident polarized light beam and plane of polarization of the wire grid polarizer are initially aligned to be coplanar. Then, more polarized light will pass through the optically readable ferroelectric memory cell when the translucent ferroelectric layer is not in an optically polarized state, than will pass through the optically readable ferroelectric memory cell when the translucent ferroelectric layer is in an optically polarized state. The sensing diode determines whether more or less light passes through the optically readable ferroelectric memory cell, to sense whether the disclosed memory cell is not in an optically polarized state or is in an optically polarized state. The condition of the optically readable ferroelectric memory cell, wherein the translucent ferroelectric layer is in an optically polarized state, can signify a binary one bit. The condition of the optically readable ferroelectric memory cell, wherein the translucent ferroelectric layer is in an optically unpolarized state, can signify a binary zero bit.
A plurality of disclosed optically readable ferroelectric memory cells is used as a memory array of a computer. Each optically readable ferroelectric memory cell stores a single binary digit, that is a bit.
Two optically readable ferroelectric memory cells are used in a differential configuration, to form a single bit storage unit. One ferroelectric memory cell is electrically written into an optically polarized state and the other ferroelectric memory cell is electrically written into an optically unpolarized state, to store a single bit. The two ferroelectric memory cells are, simultaneously, optically read out, to determine the binary value of a single bit.
An optically readable ferroelectric memory cell comprising a first translucent conductive layer, a side of a translucent ferroelectric layer, that is electrically writable into either an optically polarized state or optically unpolarized state, in parallel contact with the first translucent conductive layer, a second translucent conductive layer in parallel contact with a second side of the translucent ferroelectric layer, a first translucent insulator layer in parallel contact with a second side of the second translucent conductive layer, a side of a planar polarizer in parallel contact with a second side of the first translucent insulator layer, a second translucent insulator layer in parallel contact with a second side of the planar polarizer, and a sensing diode region within a surface of a semiconductor substrate, the sensing diode region in parallel contact with a second side of the second translucent insulator layer.